As for your question, it's like asking whether apples or oranges are the better fruit. The "Galaxy" would usually be considered the more upscale product compared with the "Costa Victoria", but that doesn't mean it's the "better" product for you.

Costa has a more international passenger mix with many European passengers (Italian, German, Swiss, French, Spanish etc.), while Celebrity has mainly English-speaking passengers. Costa offers a more relaxed experience, while Celebrity is somewhat more traditional.

I JUST GOT OFF THE GALAXY AND IT WAS MOSTLY ALL RETIRED CPL ON THE SHIP AND BY 10 PM IT WAS DEAD NOT MUCH GOING ON AFTWER 10M PM BUT IF YOU LIKE TO DRESS UP FOR YOUR MEALS THEN THIS SHIP IS FOR YOU BECAUSE YOU HAVE TO DRESS UP TO NOT ANY ANYTIME ARE JEANS AND T SHIRT OR SHORTS ALLOWED AND THE IS NOT REALLY ANY OTHER PLACE TO EAT SUPPER UNLESS YOU LIKE PIZZA OR A BURGER
THIS WAS MY FIRST AND LAST TIME WITH CRUISE LINE AS LONG AS I CAN FIND A CARNIVAL SHIP GOING THE SAME WAY

we just were on the Costa line and loved the mix of nationalities. Only about 10% were English spaking (all staff speaks English) and we thought that great. It wasn't the typical cruise and more of a European feel.Terrific food. Costa seems top offer amazing ports..